Microchip charge patterning

ABSTRACT

A method of forming a charge pattern on a microchip includes depositing a first material on an insulator surface of the microchip, depositing a material having capability of forming a self-assembled monolayer on the other material, wherein the material comprises at least one material selected from the group consisting of: octadecyltrichlorosilane, phenethyltrichlorosilane, hexamethyldisilazane, allyltrimethoxysilane, or perfluorooctyltrichlorosilanem, and patterning the self-assembled monolayer to reveal a portion of the first material. A method of forming a charge pattern in a microchip includes depositing a first material as one of either a solution processed material or a vapor deposited material to generate a first polarity or first magnitude of charge, depositing a second material as a vapor deposited material to generate a second polarity or second magnitude of charge, and immersing the microchip in a non-polar fluid comprising one selected from the group consisting of: an isoparafinnic liquid, a hydrocarbon liquid and dodecane.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Pat. Application No.16/008,961, filed Jun. 14, 2018, which is a divisional application ofU.S. Pat. Application No. 13/652,194, filed Oct. 15, 2012, now U.S. Pat.No. 10,014,261, issued Jul. 3, 2018, which are incorporated by referenceherein in their entirety.

BACKGROUND

Systems exist that assemble microchips automatically based upon somesort of encoding such as electrostatic or magnetic coding. The systemuses the encoding to identify and position the microchips as part of theassembly process.

Examples of these systems can be found in U.S. Pat. 7,861,405, and itsrelated cases, U.S. Pat. Publications 20100192365, 20100186221, and20100186222, owned by the assignee of this application. Another exampleis shown in US Patent 7,332,361, that teaches charge-encoded elementshaving basic or acidic surfaces capable of carrying charge in non-polarliquids with charge control agents. Examples include two-particleelectrophoretic ink, liquid toner, inorganic oxides, and polymers.Standard photolithography or ink-jet technology can be used to patternthese materials to form charge-encoded elements. All these referencesare incorporated by reference here. The system uses a charge or magneticpolarity on the chip to sort and position the microchips.

These references make general mention of possible methods of how chipshave the charge or polarity but give no details. For example, issues canarise with the deposition of the charge or polarity. Currently, nocurrent technique exists to deposit a charge pattern on isolatedmicrochips. One approach has charged one end of a nanowire, another hascharged up one side of a symmetric microchip, but no work appears to bedone on isolated microchips or charge patterning.

The fabrication process should be compatible with existing devices onthe chips. In addition, the process should not increase themanufacturing costs, but still allow the patterning on a scalable levelbetween larger areas and small features. To provide a flexible system,the system should allow for varying magnitudes of charge density, andideally but not necessarily, both positive and negative polarity, formultiple levels of chip control and identification. The charge patternsshould have good stability to allow long shelf life of the patterneddevices.

Another issue with patterning may arise with the chips being attractedto each other. They may gather together or conglomerate based upon theirrespective charges. The density of the chips needs to remain low enoughthe chips do not exchange charge by contact with each other.

SUMMARY

According to aspects illustrated here, there is provided a method offorming a charge pattern on a microchip including depositing a firstmaterial on an insulator surface of the microchip, depositing a materialhaving the capability of forming a self-assembled monolayer on the othermaterial, wherein the material comprises at least one material selectedfrom the group consisting of: octadecyltrichlorosilane,phenethyltrichlorosilane, hexamethyldisilazane, allyltrimethoxysilane,or perfluorooctyltrichlorosilanem, and patterning the self-assembledmonolayer to reveal a portion of the first material.

According to aspects illustrated here, there is provided a method offorming a charge pattern in a microchip including depositing a firstmaterial as one of either a solution processed material or a vapordeposited material to generate a first polarity or first magnitude ofcharge, depositing a second material as a vapor deposited material togenerate a second polarity or second magnitude of charge, and immersingthe microchip in a non-polar fluid comprising one selected from thegroup consisting of: an isoparafinnic liquid, a hydrocarbon liquid anddodecane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an overall method of forming chargepatterns on microchips.

FIG. 2 shows an embodiment of a method of forming charge patterns on amicrochip.

FIG. 3 shows an embodiment of a method of printing charge patterns on amicrochip.

FIGS. 4-7 show an embodiment of a method of photolithographicallyforming charge patterns on a microchip.

FIGS. 8-10 show an embodiment of a method of forming a charge patternusing a scorotron.

FIGS. 11-13 show an embodiment of a method of forming a bipolar chargetemplate.

FIGS. 12-16 show an alternative embodiment of a method of forming abipolar charge template.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows an overall embodiment of a method of forming chargepatterns on a microchip. At 11, the microchips are fabricated on asubstrate, such as silicon, gallium arsenide, complementary metal oxidesemiconductor (CMOS) etc. The process then deposits materials on themicrochips to enable charging at 13. In one approach, shown in moredetail in FIGS. 2-7 , the microchips are then submersed in a fluid thatcauses charge to develop on the materials deposited. In anotherapproach, shown in more detail in FIGS. 8-16 , the materials on themicrochips are charged using an external device. The end result ismicrochips with charge patterns on their surfaces in 19.

FIG. 2 shows an embodiment of a method of forming charge patterns on amicrochip. The process will more than likely begin at the wafer level at10, after manufacture of the individual microchips on the wafer. Thisallows the process of charge patterning to occur in a more mass-producedmanner, using techniques compatible with chip fabrication processes.However, no limitation is intended by this discussion, and none shouldbe implied. The individual chips can be patterned using the sametechniques after singulation from the wafer.

Using manufacturing techniques compatible with chip processing, themanufactured microchip 12 has a shield 14 to protect the circuitry onthe chip. The shield has an insulator 16. The insulator allows charge ormaterial patterns deposited on the surface to avoid interaction with thecircuitry on the microchip. The pattern ABBAB may represent differentcharges, such as + --+ -, or a pattern of materials into which chargewill be developed. Through the techniques discussed in more detailfurther, the charge pattern may consist of alternating regions ofdiffering charge magnitude and/or polarity. The embodiment in thisportion of the discussion has the patterns being charge.

Once singulated, the microchips can be placed into a fluid to create an‘ink’ bottle 22 or other dispenser. The fluid may contain otheradditives such as a charge control agent. The charge control agent mayeither allow the charge to remain stable on the surface of the chips 12,or may cause the charge to develop on the surface of the wafer. Thecharge generation may take the form of depositing a material, anddeveloping a charge in the material thorough the interaction of thecharge patterning material with the fluid component of the ink.

One approach uses deposition of a thin-film of the charge patterningmaterial using solution processing techniques such as spin-coating,printing, dip-coating or self-assembly, or vapor deposition techniquessuch as plasma enhanced chemical vapor deposition (PECVD) or atomiclayer deposition (ALD), followed by immersion in solution afterdeposition of the film. Examples of materials that could be deposited bysolution or vapor techniques include polymers such as polyethylene,polystyrene, polymethylmethacrylate, and parylene and polyvinylalcohol,as well as cationic and anionic polyelectrolytes such aspolystyrenesulfonic acid, polyallylamine, polyacrylic acid, andpoly(diallyldimethylammonium chloride). Other examples includeorganometallic salts such as zinc stearate or aluminum stearate as wellas oxides, such as silica, alumina or titania. In addition materialswhich form self-assembled monolayers such as octadecyltrichlorosilane,phenethyltrichlorosilane, hexamethyldisilazane, allyltrimethoxysilane orperfluorooctyltrichlorosilane may also be used.

The charge patterning material may not be a pure material but rather ablend of one or more materials, possibly to enhance charge generatingproperties, improve processing performance, or impart new functionalityto the film such as making it light sensitive. For materials depositedfrom solution, they would likely be first dissolved in a solvent such astoluene, hexane, water, isopropanol, or tetrahydrofuran to enablesolution processing. An example process may involve spin coating thematerial onto the surface of the microchip, patterning the materialeither using light directly if a light-sensitive formulation of thecharge-patterning material is used, or in a separate step throughphotolithographic/etching cycles, and immersing the chip into solutionwhere free charges are formed through interaction between the fluid andthe material.

In FIG. 4 , a first polymer is spun onto the insulator 16 andphotolithographically defined in FIG. 5 , exposing a portion of theinsulator 16. A second polymer 42 is then spun on or otherwise depositedon the first polymer and the exposed insulator in FIG. 6 . The secondpolymer is then patterned to define a region separate from the firstregion, typically with a region of the insulator. The two differentpolymers then retain different charges, or magnitudes of charge to forma charge pattern. In addition to the use of two solution processedpolymers, other embodiments may use a combination of a solutionprocessed material to generate one polarity/magnitude of charge and avapor deposited material to generate another polarity/magnitude ofcharge, other embodiments could use two different vapor depositedmaterials.

If immersed in a polar liquid, such as water, most surfaces becomecharged, as some of the surface molecules dissociate. Charge tends to bemore negative or positive depending on the chemical composition of thesurface. Typical functional groups that develop a negative surfacechange include sulfonic acids, phosphonic acids, and carboxylic acidsamongst others. Typical functional groups that develop positive surfacecharges include amines and imidazoles, amongst others. The range ofCoulomb interaction of the charged microchips is controlled by the ionicstrength of the solution, but is typically rather short, in the range of1 to 10 micrometers due to the high ion content.

In this embodiment the use of non-polar fluids is desired however, sincesuch Coulomb interactions between charged entities are felt over muchlarger length scales, in the range of 10-100 micrometers. Examples ofnon-polar fluids include isoparaffinic liquids such as the isopar seriesof fluids, and other hydrocarbon liquids such as dodecane. In non-polarliquids charge control agents, typically amphiphilic surfactantmaterials (both ionic and non-ionic), such as phosphatidylcholine(lecithin), sorbitan monooeleate (span-80), aluminium-di-tert-butylsalicylate (ALOHOS), polyisobutylene succinimide (OLOA), or sodiumdioctylsulfosuccinate (AOT) amongst others may need to be added to theliquid to assist in developing charge.

If the surrounding liquid is air, charging of the surface can be donethrough tribo-actions. For example, in Xerography, the toner particlesare charged by contacting specifically designed developer particles. Thecharge patterning material has to be selected such that it charges inspecific ways when contacted with the developer material. The density ofthe chips should stay low enough to control charge exchange betweenmicrochips accidentally hitting each other.

In another approach, shown in FIG. 3 , an ink-jet head 30 can depositthe charge-patterning material. Candidate material may include waxes,polymers, such as polyelectrolytes, or blends of materials amongstothers. After deposition of the charge patterning material, as inprevious descriptions the chips would be singulated and immersed in afluid where free charges would be generated.

In another approach, a self-assembled monolayer can be used along withanother material, such as an oxide, to create charged regions on thechip. This could be accomplished, for example, by first depositing theoxide, then depositing the self-assembled monolayer having the desiredfunctionality over the oxide. Using photolithography and etching thisself-assembled monolayer could then be patterned revealing the oxideunderneath. In another approach, the oxide could be deposited followedby patterning of a sacrificial blocking material (such as photoresist),deposition of the self-assembled monolayer could then take place,followed by removal of the sacrificial material, again revealing theunderlying oxide surface, creating an oxide, self-assembled monolayerpattern. This second approach has the benefit in that the self-assembledmonolayer deposition and blocking material removal steps can be carriedout either at the wafer scale, or at the chiplet scale after wafersingulation.

FIGS. 4-7 show processes of an embodiment in which photolithographicpatterned polymers, inorganic materials or a mixture of the two areused. These materials can either be tribo-charged or chemically chargedusing a charge control agent, in a dielectric fluid to carry differentpolarities of charge. Photolithographic defined charging of a dielectricwith a corona device is another approach, using dry film resist.Commercially available dry film resists express substantial conductivitydifference between exposed ultraviolet and unexposed regions. FIGS. 4-7show a process for photolithographic materials.

In a photoconductor coating embodiment, one may use inorganicphotoconductor materials such as amorphous silicon and selenium, orsingle layer or multilayer organic photoconductors. If such aphotoconductor coating is used, it receives charge from a corotron orscorotron to give the desired charge signs and patterns. As the termsare used here, a corotron is a corona charging device typically used inelectrophotography/Xerography that has a wire connected to a highvoltage power source. In a typical application, the wire generates anelectric field that charges up a photoreceptor in preparation forreceiving charged toner particles. A scorotron is a screen corotron.

Another embodiment uses photolithographic define charging of adielectric with a corona device. Commercially available dry film resistexpresses substantially conductivity difference between ultravioletexposed and unexposed regions. FIGS. 8-10 show one embodiment of such aprocess. In FIG. 8 , a dry film resist is laminated onto the insulatorlayer 16 over the microchip or microchip wafer 12. In FIG. 9 ,ultraviolet light exposes a portion 52 of the dry resist, creating highand low conductivity regions. In FIG. 10 , the wafer or microchip 12 isgrounded by connection 54 and charged with a scorotron or corotron 56,to form charge patterns based upon the previously exposed regions 50 and52 of the dry film resist. This forms a single charge template, wherethe surface has one polarity of charge. One may verify the chargepatterns by spreading beads of known charge and imaging with a camera ormeasuring the field directly in air with a non-contact electrostaticvolt meter.

FIGS. 11-13 show an embodiment of a method of forming a dual chargetemplate. Ultraviolet light exposes a portion of the dry film resist 50to form a low conductivity region 52. Using a stencil mask 62 on top ofthe dry film resist allows exposure of only a portion of the lowconductivity region formed by the UV exposure. The scorotron 64 appliescharge of a first polarity to a portion of the low conductivity regionnot protected by the mask 62. The process shifts the mask 62 to coverthe charged portion of the low conductivity region. The scorotron thencharges the uncharged portion of the low conductivity region with alower dose of the opposite sign ions to create the other sign chargepattern. To differentiate between the two scorotron processes, theopposite sign charge pass of the scorotron is referred to as 66.

In an alternative embodiment, a bipolar or a dual charge template canresult from a dual exposure, shown in FIGS. 14-16 . FIG. 14 shows afirst exposure forming a first low conductivity region 52 on the dryfilm resist 50. This first region then receives a first polarity chargefrom a scorotron 62. The dry film resist then receives a second exposureof UV light to form a second low conductivity region 70. This secondregion then receives a charge of the opposite polarity from thescorotron 64.

In this manner, charge patterns can be generated on the surface ofmicrochips, either before or after singulation from a wafer. Thetechniques used are compatible with semiconductor fabrication processes,either using scorotron or corotron charging, tribo-charging, or byapplication of charged materials. Free charges may then be generateddirectly or through the interaction of these materials with thesurrounding fluid in the chip “ink.” The charge patterns containinformation usable in automated systems to sort, organize and arrangemicrochips into larger circuits.

It will be appreciated that several of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations, or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

What is claimed is:
 1. A method of forming a charge pattern on a microchip, comprising: depositing a first material on an insulator surface of the microchip; depositing a material having the capability of forming a self-assembled monolayer on the other material, wherein the material comprises at least one material selected from the group consisting of: octadecyltrichlorosilane, phenethyltrichlorosilane, hexamethyldisilazane, allyltrimethoxysilane, or perfluorooctyltrichlorosilane; and patterning the self-assembled monolayer to reveal a portion of the first material.
 2. The method as claimed in claim 1, wherein the first material comprises an oxide.
 3. The method as claimed in claim 1 wherein depositing the first material comprises: first depositing an oxide on an insulator surface of the microchip; and patterning a sacrificial blocking material onto a portion of the oxide as the first material; and removing the sacrificial blocking material after depositing the self-assembled monolayer to reveal the oxide.
 4. The method as claimed in claim 3, wherein the blocking material comprises photoresist.
 5. The method as claimed in claim 3, wherein the method is performed at one of with the chiplet scale or the wafer scale.
 6. A method of forming a charge pattern in a microchip, comprising: depositing a first material as one of either a solution processed material, or a vapor deposited material to generate a first polarity or first magnitude of charge; depositing a second material as a vapor deposited material to generate a second polarity or second magnitude of charge; and immersing the microchip in a non-polar fluid comprising one selected from the group consisting of: an isoparafinnic liquid, a hydrocarbon liquid and dodecane.
 7. The method as claimed in claim 6, wherein depositing the first material comprises depositing a solution process material.
 8. The method as claimed in claim 6, wherein depositing the first material comprises depositing a vapor deposited material.
 9. The method as claimed in claim 6, wherein the first material comprises at least one selected from the group consisting of: polyethylene, polystyrene, polymethylmethacrylate, parylene, polyvinylalcohol, cationic and anionic polyelectrolytes, polystyrene-sulfonic acid, polyallylamine, polyacrylic acid, poly(diallyldimethylammonium chloride), organometallic salts, zinc stearate, aluminum stearate, silica oxide, alumina oxide, or titania oxide. 